Thermoplastic elastomers exhibiting superior barrier properties

ABSTRACT

A blend of styrene-isobutylene-styrene based thermoplastic elastomer and organoclay-filled polyamide is disclosed which has good processability and more effective barrier properties for oxygen than the blend using amorphous or crystalline polyamide without organoclay.

CLAIM OF PRIORITY

This application claims priority from U.S. Provisional PatentApplication Ser. No. 61/047,047 bearing Attorney Docket Number 12008012and filed on Apr. 22, 2008, which is incorporated by reference.

FIELD OF THE INVENTION

This invention relates to thermoplastic elastomers containingorganoclay-filled polyamide to provide barrier properties.

BACKGROUND OF THE INVENTION

The world of polymers has progressed rapidly to transform materialscience from wood and metals of the 19^(th) Century to the use ofthermoset polymers of the mid-20^(th) Century to the use ofthermoplastic polymers of later 20^(th) Century.

An example of a popular rubber is butyl rubber which has excellent gasbarrier properties. But butyl rubber is not capable of being injectionmolded.

Thermoplastic elastomers (TPEs) combine the benefits of elastomericproperties of thermoset polymers, such as vulcanized rubber, with theprocessing properties of thermoplastic polymers. Therefore, TPEs arepreferred because they can be made into articles using injection moldingequipment. But often, TPEs lack gas barrier properties comparable tobutyl rubber.

U.S. Pat. No. 7,150,294 (Katayama et al.) discloses a two layer hosewith an outer layer of a blend of styrene-isobutylene block copolymerand polyamide, and preferably also including a compatibilizer.

SUMMARY OF THE INVENTION

What the art needs is a new formulation of thermoplastic elastomer (TPE)that has gas barrier properties approaching those of butyl rubber.

The present invention solves that problem by using a TPE formulationthat includes organoclay-filled polyamide.

One aspect of the invention is a thermoplastic elastomer compound,comprising (a) styrene-isobutylene-styrene and (b) polyamide includingorganoclay dispersed in the polyamide.

Features of the invention will become apparent with reference to thefollowing embodiments.

EMBODIMENTS OF THE INVENTION TPE-S

One type of TPE is based on styrene (also called “TPE-S”). The presentinvention uses a TPE-S based on styrene-isobutylene-styrene (“SIBS”) asthe matrix polymer for the TPE. A commercial source of SIBS is Kaneka ofJapan. SIBS is becoming increasingly popular as a high-value TPE-S, asnoted in U.S. Pat. No. 7,150,294 (Katayama et al.)

Typically, commercial grades of TPE-S are a complex combination of TPE,plasticizer, processing aid (mold release agent), filler, antioxidant,and one or more secondary polymers, such as polyolefins.

Polyamide as Secondary Polymer

In the present invention, the TPE-S includes polyamide as a secondarypolymer. The polyamide can be amorphous or crystalline. Any amorphous orcrystalline polyamide among the following list is a candidate for use inthis invention: polyamide 6; polyamide 6,6; polyamide 9,9; polyamide6,10; polyamide 6,12; polyamide 11; polyamide 9,10; polyamide 9,12;polyamide 12; a copolymer of polyamide 6 and polyamide 6,6; a copolymerof polyamide 6 and polyamide 12; and combinations thereof.

Regardless of the polyamide employed, the polyamide needs to havedispersed therein an organoclay. Despite the considerable difference incohesive energy densities between SIBS and polyamide, an organoclayfilled polyamide (“Nanonylon” for convenience in this application)provides unexpected superior barrier properties over even that of SIBSand polyamide alone, which itself is a considerable improvement overSIBS alone.

Organoclay

Organoclay is obtained from inorganic clay usually from the smectitefamily. Smectites have a unique morphology, featuring one dimension inthe nanometer range. Montmorillonite clay is the most common member ofthe smectite clay family. The montmorillonite clay particle is oftencalled a platelet, meaning a sheet-like structure where the dimensionsin two directions far exceed the particle's thickness.

Inorganic clay becomes commercially significant if intercalated with anorganic intercalant to become an organoclay. An intercalate is aclay-chemical complex wherein the clay gallery spacing has increased,due to the process of surface modification by an intercalant. Under theproper conditions of temperature and shear, an intercalate is capable ofexfoliating in a resin polyolefin matrix. An intercalant is an organicor semi-organic chemical capable of entering the montmorillonite claygallery and bonding to the surface. Exfoliation describes a dispersionof an organoclay (surface treated inorganic clay) in a plastic matrix.In this invention, organoclay is exfoliated at least to some extent.

In exfoliated form, inorganic clay platelets have a flexible sheet-typestructure which is remarkable for its very small size, especially thethickness of the sheet. The length and breadth of the particles rangefrom 1.5 μm down to a few tenths of a micrometer. However, the thicknessis astoundingly small, measuring only about a nanometer (a billionth ofa meter). These dimensions result in extremely high average aspectratios (200-500). Moreover, the miniscule size and thickness mean that asingle gram contains over a million individual particles.

Nanocomposites are the combination of the organoclay and the plasticmatrix. In this invention, Nanonylon is the nanocomposite which providesthe unexpected results. In polymer compounding, a nanocomposite is avery convenient means of delivery of the organoclay into the ultimatecompound, provided that the plastic matrix is compatible with theprincipal polymer resin components of the compounds. In such manner,nanocomposites are available in concentrates, masterbatches, andcompounds from CP Polymers of Pasadena, Calif., Nanocor, Inc. ofArlington Heights, Ill. (www.nanocor.com) and PolyOne Corporation ofAvon Lake, Ohio (www.polyone.com) in a variety of nanocomposites.Particularly preferred organoclays are I24TL, I30P, I44P, and I44W fromNanocor, Inc. which can then be dispersed into amorphous or crystallinepolyamide.

Nanocomposites offer flame-retardancy properties because suchnanocomposite formulations burn at a noticeably reduced burning rate anda hard char forms on the surface. They also exhibit minimum dripping andfire sparkling.

Nanocomposites also have improved barrier properties as compared withthe plastic matrix without organoclay.

The amount of organoclay in the Nanonylon can range from about 1 toabout 8 weight percent, and preferably from about 3 to about 8 weightpercent.

Optional Additives

The compound of the present invention can include conventional plasticsadditives in an amount that is sufficient to obtain a desired processingor performance property for the compound. The amount should not bewasteful of the additive nor detrimental to the processing orperformance of the compound. Those skilled in the art of thermoplasticscompounding, without undue experimentation but with reference to suchtreatises as Plastics Additives Database (2004) from Plastics DesignLibrary (www.williamandrew.com), can select from many different types ofadditives for inclusion into the compounds of the present invention.

Non-limiting examples of optional additives include adhesion promoters;biocides (antibacterials, fungicides, and mildewcides), anti-foggingagents; anti-static agents; bonding, blowing and foaming agents;dispersants; fillers and extenders; fire and flame retardants and smokesuppresants; impact modifiers; initiators; lubricants; micas; pigments,colorants and dyes; oils and plasticizers; processing aids; releaseagents; silanes, titanates and zirconates; slip and anti-blockingagents; stabilizers; stearates; ultraviolet light absorbers; viscosityregulators; waxes; and combinations of them.

Table 1 shows the acceptable and desirable ranges of ingredients for theTPE-S of the present invention. All but the SIBS and Nanonylon areoptional for the present invention.

TABLE 1 Ranges of Ingredients Ingredient (Wt. Percent) AcceptableDesirable SIBS 20-90%  30-85% Nanonylon  5-50%  10-30% Plasticizer 0-70%   0-50% Other Polymer(s)  0-50%   0-15% Processing Aid-  0-2% 0-0.5% Mold Release Filler  0-40%   0-15% Anti-oxidant  0-1%  0-0.2%Other Optional  0-10%   0-5% Additives

Processing

The preparation of compounds of the present invention is uncomplicated.The compound of the present can be made in batch or continuousoperations.

Mixing in a continuous process typically occurs in an extruder that iselevated to a temperature that is sufficient to melt the polymer matrixwith addition either at the head of the extruder or downstream in theextruder of the solid ingredient additives. Plasticizer oil can bepre-mixed with the SEBS, if SEBS is included in the formulation, in aribbon blender or optionally added downstream by injection. Extruderspeeds can range from about 50 to about 500 revolutions per minute(rpm), and preferably from about 100 to about 300 rpm. Typically, theoutput from the extruder is pelletized for later extrusion or moldinginto polymeric articles.

Mixing in a batch process typically occurs in a Banbury mixer that isalso elevated to a temperature that is sufficient to melt the polymermatrix to permit addition of the solid ingredient additives. The mixingspeeds range from 60 to 1000 rpm and temperature of mixing can beambient. Also, the output from the mixer is chopped into smaller sizesfor later extrusion or molding into polymeric articles.

Subsequent extrusion or molding techniques are well known to thoseskilled in the art of thermoplastics polymer engineering. Without undueexperimentation but with such references as “Extrusion, The DefinitiveProcessing Guide and Handbook”; “Handbook of Molded Part Shrinkage andWarpage”; “Specialized Molding Techniques”; “Rotational MoldingTechnology”; and “Handbook of Mold, Tool and Die Repair Welding”, allpublished by Plastics Design Library (www.williamandrew.com), one canmake articles of any conceivable shape and appearance using compounds ofthe present invention.

USEFULNESS OF THE INVENTION

TPE-S of the present invention, based on SIBS and Nanonylon provides gasbarrier properties comparable to butyl rubber. As such, and with theadvantage of being capable of being injection molded, plastic articlescan be made from formulations of the present invention for such uses asseals, closures, and other articles previously made from butyl rubber.Other articles can be made from the TPE-S nanocomposites of the presentinvention, such as the following industrial and consumer products: foodand drink container seals, printer cartridge seals, medical containerseals, baby pacifiers, and other products needing both flexibility andbarrier properties, as a suitable replacement for butyl rubber.

EXAMPLES

Table 2 shows two examples of the present invention, in comparison witha control (Comparative Example A) and four comparison examples(Comparative Examples B-E) representing a TPE-S with either amorphous orcrystalline nylon which does not contain organoclay.

All formulations of Examples 1-2 and Comparative Examples A-E had thesame SIBS TPE-S matrix. All formulations of Examples 1-2 and ComparativeExamples B-E had the same SIBS TPE-S matrix and antioxidant. ComparativeExamples B and D offered a direct comparison with Example 1, whileComparative Examples C and E offered a direct comparison with Example 2.Only the type of polyamide was different.

All of Examples 1-2 and B-E were made using a twin-screw extruder set at238° C. in all zones, rotating at 500 rpm. All ingredients were addedbefore Zone 1. The melt-mixed compound was pelletized for furtherhandling.

Pellets of all Examples 1-2 and A-E were molded into tensile test barsusing a Demag injection molding machine, operating at 190° C.temperature and high pressure. Table 3 shows experimental results.

TABLE 2 Formulations Ingredient/Commercial Source (Parts by Weight)Purpose Comp. A Comp. B Comp. C Comp. D Comp. E 1 2 Sibstar 073T SIBSTPE-S 100 85 70 85 70 85 70 (Mw = 83,000) (Kaneka, Japan) Matrix Selar3426 Amorphous polyamide Barrier 15 30 (DuPont, Wilmington, DE, USA)Ultramid 8202 polyamide 6 (BASF, Barrier 15 30 Florham Park, NJ, USA)CRESS-ALON A NE2740 Injection Barrier 15 30 Grade Nanonylon (CPPolymers, Pasadena, CA, USA) (Contains polyamide 6 and 4% organoclay)Irganox 1010 Antioxidant Antioxidant/ 0.1 0.1 0.1 0.1 0.1 0.1 (Ciba,Switzerland) UV package

TABLE 3 Physical Properties Ingredient/Commercial Source (Parts byWeight) Comp. A Comp. B Comp. C Comp. D Comp. E 1 2 Shore A Hardness 5055 64 56 70 68 89 (ASTM D2240, 10 s delay) Specific Gravity (ASTM D792)0.96 0.99 1.01 0.97 1.00 0.97 0.99 Tensile Strength, psi (ASTM D412, DieC) 1195 1431 1816 1391 1779 1196 1855 Elongation, % (ASTM D412, Die C)422 254 151 327 226 292 83 Tear Strength, pli (ASTM D624) 155 135 158166 296 234 386 Oxygen Transmission Rate (OTR), cc · mil/m² · day 30101880 1210 1610 410 570 55 (ASTM D3985) Percent OTR Improvement ofExample 1 Over  528% 329% 282% Comparative Examples A, B, and D PercentOTR Improvement of Example 2 Over 5472% 2200% 745% Comparative ExamplesA, C, and E

Table 3 shows the physical properties of Examples 1-2 and ComparativeExamples A-E are comparable or manageable for Shore A hardness, SpecificGravity, Tensile Strength, Percent Elongation, and Tear Strength.

What is totally unexpected is the amount of oxygen transmission ratedecrease in Examples 1 and 2, when compared to neat SIBS (ComparativeExample A) or SIBS and amorphous nylon (Comparative Examples B and C) orSIBS and crystalline nylon (Comparative Examples D and E).

Example 1 with Nanonylon at 15 parts by weight has two to three timesthe oxygen barrier performance over use of amorphous or crystallinenylon at the same weight percent. Example 2 with Nanonylon at 30 partsby weight has seven to 22 times the oxygen barrier performance over useof amorphous or crystalline nylon at the same weight percent.

Therefore, using Examples 1 and 2 and other explanations of the presentinvention in this document, one of ordinary skill in the art, withoutundue experimentation, will be able to formulate to achieve theappropriate balance of physical processing and physical performanceproperties while at the same time achieving extraordinarily andunexpectedly superior oxygen barrier properties.

The invention is not limited to the above embodiments. The claimsfollow.

What is claimed is:
 1. A thermoplastic elastomer compound, comprising:(a) styrene-isobutylene-styrene (SIBS) and (b) polyamide includingorganoclay dispersed in the polyamide.
 2. The compound of claim 1,further comprising plasticizer oil.
 3. The compound of claim 1, furthercomprising filler.
 4. The compound of claim 1, further comprisingadditives selected from the group consisting of adhesion promoters;biocides (antibacterials, fungicides, and mildewcides), anti-foggingagents; anti-static agents; bonding, blowing and foaming agents;dispersants; fillers and extenders; fire and flame retardants and smokesuppresants; impact modifiers; initiators; lubricants; micas; pigments,colorants and dyes; oils and plasticizers; processing aids; releaseagents; silanes, titanates and zirconates; slip and anti-blockingagents; stabilizers; stearates; ultraviolet light absorbers; viscosityregulators; waxes; and combinations of them.
 5. The compound of claim 1,wherein the SIBS comprises from about 20 to about 90 weight percent ofthe compound and wherein the organoclay dispersed polyamide comprisesfrom about 5 to about 50 weight percent of the compound.
 6. The compoundof claim 1, wherein the organoclay is exfoliated within the polyamide,and wherein the organoclay comprises between about 1 and about 8 weightpercent of a combination of organoclay dispersed polyamide.
 7. A moldedarticle, comprising a compound of claim
 1. 8. A method of using thecompound of claim 1, wherein the method comprises the step of moldingthe compound into an article that has more than about 280% improvementin reduced oxygen transmission than a compound which has the same SIBSand polyamide but no organoclay.
 9. The compound of claim 2, furthercomprising filler.
 10. The compound of claim 2, further comprisingadditives selected from the group consisting of adhesion promoters;biocides (antibacterials, fungicides, and mildewcides), anti-foggingagents; anti-static agents; bonding, blowing and foaming agents;dispersants; fillers and extenders; fire and flame retardants and smokesuppresants; impact modifiers; initiators; lubricants; micas; pigments,colorants and dyes; oils and plasticizers; processing aids; releaseagents; silanes, titanates and zirconates; slip and anti-blockingagents; stabilizers; stearates; ultraviolet light absorbers; viscosityregulators; waxes; and combinations of them.
 11. The compound of claim2, wherein the SIBS comprises from about 20 to about 90 weight percentof the compound and wherein the organoclay dispersed polyamide comprisesfrom about 5 to about 50 weight percent of the compound.
 12. Thecompound of claim 2, wherein the organoclay is exfoliated within thepolyamide, and wherein the organoclay comprises between about 1 andabout 8 weight percent of a combination of organoclay dispersedpolyamide.
 13. The molded article of claim 7, wherein the compoundfurther comprises filler.
 14. The molded article of claim 7, wherein thecompound further comprises additives selected from the group consistingof adhesion promoters; biocides (antibacterials, fungicides, andmildewcides), anti-fogging agents; anti-static agents; bonding, blowingand foaming agents; dispersants; fillers and extenders; fire and flameretardants and smoke suppresants; impact modifiers; initiators;lubricants; micas; pigments, colorants and dyes; oils and plasticizers;processing aids; release agents; silanes, titanates and zirconates; slipand anti-blocking agents; stabilizers; stearates; ultraviolet lightabsorbers; viscosity regulators; waxes; and combinations of them. 15.The molded article of claim 7, wherein the SIBS comprises from about 20to about 90 weight percent of the compound and wherein the organoclaydispersed polyamide comprises from about 5 to about 50 weight percent ofthe compound.
 16. The molded article of claim 7, wherein the organoclayis exfoliated within the polyamide, and wherein the organoclay comprisesbetween about 1 and about 8 weight percent of a combination oforganoclay dispersed polyamide.
 17. The method of claim 8, wherein thecompound further comprises filler.
 18. The method of claim 8, whereinthe compound further comprises additives selected from the groupconsisting of adhesion promoters; biocides (antibacterials, fungicides,and mildewcides), anti-fogging agents; anti-static agents; bonding,blowing and foaming agents; dispersants; fillers and extenders; fire andflame retardants and smoke suppresants; impact modifiers; initiators;lubricants; micas; pigments, colorants and dyes; oils and plasticizers;processing aids; release agents; silanes, titanates and zirconates; slipand anti-blocking agents; stabilizers; stearates; ultraviolet lightabsorbers; viscosity regulators; waxes; and combinations of them. 19.The method of claim 8, wherein the SIBS comprises from about 20 to about90 weight percent of the compound and wherein the organoclay dispersedpolyamide comprises from about 5 to about 50 weight percent of thecompound.
 20. The method of claim 8, wherein the organoclay isexfoliated within the polyamide, and wherein the organoclay comprisesbetween about 1 and about 8 weight percent of a combination oforganoclay dispersed polyamide.